LED light source with lens

ABSTRACT

The light source has an LED, preferably produced for the surface-mounting technique, embedded in a transparent material filling. A converter substance is integrated in the filling for the at least partial wavelength conversion of the light emitted by the LED. A lens is glued onto the transparent material filling. The material filling has a convex surface and the lens has a concave underside entering into a form fit with the convex surface of the material filling.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of U.S. application Ser. No. 10/007,398, filed Oct.22, 2001 now U.S. Pat. No. 6,759,803, which was a continuation ofInternational Application PCT/DE00/01079, filed Apr. 7, 2000, whichdesignated the United States, and which was not published in English.This application also claims the benefit of German application 199 18370.8, filed Apr. 22, 1999. All prior applications are herewithincorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a light source and, more particularly, to anLED light source, with at least one LED, a basic body formed with arecess wherein the LED is arranged, a filling of transparent materialwhich embeds the LED and wherein a converter substance for the at leastpartial wavelength conversion of the light emitted by the LED iscontained, and a lens in contact with the material filling.

LEDs (light-emitting diodes) based on GaN, with which blue orultraviolet light can be generated, have recently been developed. Withthe aid of these LEDs, light sources can be produced on the basis ofwavelength conversion. A concept, which has already been realizedprovides that part of the blue light emitted from the LED is convertedinto yellow light by a suitable converter material, so that white lightis generated as a consequence of the resultant color mixing of theoriginal blue light with the converted yellow light. In a secondconcept, it is proposed to convert ultraviolet light of a suitable LEDinto the visible spectral range.

The converter material, in the case of both concepts, may either becontained in the semiconductor material of the LED or in an embeddingmaterial of resin or the like surrounding the LED.

To increase the radiation intensity of the component in the emissiondirection, the LED components may be provided with an optical lens, bywhich the light is focused and emitted in a directed manner.

An example of a form of construction of this type is represented inFIG. 1. There, a form of LED construction is illustrated that isdescribed, for example, in the article “SIEMENS SMT-TOPLED für dieOberflächenmontage” [SIEMENS SMT-TOPLED for surface mounting] by F.Möllmer and G. Waitl in the Journal Siemens Components 29 (1991), issue4, page 147 in connection with FIG. 1. That form of LED is extremelycompact and, if appropriate, allows the arrangement of a large number ofLEDs of this type in a linear array or a matrix array.

In the case of a SMT-TOPLED of the configuration shown in FIG. 1, an LED2 is mounted with one of its electrical contact areas on a leadframe 5,which is connected to one pole of a voltage source, while an oppositeleadframe 5, connected to the other pole of the voltage source, isconnected by a bonding wire 6 to the other electrical contact area ofthe LED 2. The two leadframes 5 are encapsulated in ahigh-temperature-resistant thermoplastic. In this way, a basic body 1,wherein there is a recess 1A into which the LED 2 protrudes from theinside is formed by injection molding. The thermoplastic preferably hasa high diffuse reflectance of approximately 90%, so that the lightemitted by the LED 2 can be additionally reflected at the sloping sidewalls of the recess 1A in the direction of the outlet opening. Therecess 1A is filled with a transparent resin material 3, such as anepoxy resin, which contains a converter material, for example a suitabledye. The resin material and the thermoplastic are carefully matched witheach other, in order that even peak thermal loads do not lead tomechanical problems.

During operation, blue or ultraviolet light is emitted by the LED 2,which may be produced for example on the basis of GaN or on the basis ofII–VI compounds. On its path from the LED 2 to the lens 4, therelatively short-wave emitted light radiation is partially convertedinto longer-wave light radiation in the resin filling 3 containing theconverter material. In particular, if a blue LED is used, such aconverter material by which the blue light radiation is converted atleast partially into yellow light radiation can be used. One problem ofthis type of construction, however, is that the light rays are subjectto different path lengths in the resin filling 3 filled with theconverter material from the LED 2 to the lens 4. These have the resultthat the yellow fraction in the light radiation predominates in theouter region of the component, whereas by contrast, the blue fraction inthe light radiation predominates in the center. This effect consequentlyleads to a color locus of the emitted light radiation varying with thedirection of emission or direction of viewing.

U.S. Pat. No. 3,875,456 discloses semiconductor light sources which havetwo semiconductor elements arranged in a housing or reflector. Thesemiconductor elements are embedded in a scattering layer, downstream ofwhich there is a covering formed similar to a lens. The scattering layerand the covering may be formed by resin layers applied one on top of theother and contain phosphorescent materials.

U.S. Pat. No. 5,847,507 describes a light-emitting diode wherein thesemiconductor element is enveloped by a covering in lens form, forexample of epoxy resin, which contains fluorescent materials.

European patent publication EP 0 230 336 shows a component which has asubstrate on which an annular spacer and an optoelectronic element arefastened. The optoelectronic element is arranged inside the annularopening. The annular opening is filled with a transparent compound andis closed off by a spherical lens, which is mounted on the annularspacer, lying opposite the substrate, and is in contact with thetransparent compound.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide an LED lightsource, which overcomes the above-mentioned disadvantages of theheretofore-known devices and methods of this general type and whereinthe path length of the radiation through the converter material isessentially equal and the light radiation can be emitted in a focusedform. In addition, a method of producing a light source of this type isto be specified.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a LED light source. The light sourcecontains a basic body having a recess formed therein, and only one LEDis disposed in the recess and emits light of a first wavelength. Afilling of a transparent material embeds the LED. The transparentmaterial has a converter substance for at least partially converting thelight emitted by the LED into light having a second wavelength. Thelight of the first wavelength and the light of the second wavelength aremixed. A lens is in contact with the filling. The lens has a concaveunderside, whereby an upper side of the filling enters into a form fitwith the concave underside of the lens and has a convex surface formedby the underside of the lens.

In accordance with an added feature of the invention, a volume of thefilling is less than a free volume of the recess with the LED disposedtherein.

In accordance with an additional feature of the invention, the convexsurface of the filling and the underside of the lens are formed to havea substantially constant distance from the LED.

In other words, the filling has a convex upper surface defined bysubstantially equidistant points from the LED, i.e., it is approximatelyspherical with the LED forming the center of the sphere.

In accordance with another feature of the invention, the LED has anactive radiating area and the convex surface of the filling and theunderside of the lens are formed at a substantially constant distancefrom a geometrical center point of the active radiating area of the LED.

In accordance with a further feature of the invention, the LED is a bluelight-emitting LED based on GaN and the converter substance convertslight radiation in the blue spectral range into light radiation in theyellow spectral range. In an alternative embodiment, the LED is aUV-emitting LED and the converter substance converts UV light into avisible spectral range.

In accordance with again an added feature of the invention, a distanceof the convex surface from the LED is set such that a degree ofconversion along an optical path length of the light radiation issubstantially 50%.

In accordance with again an additional feature of the invention, the LEDhas an active radiating area and a distance of the convex surface from ageometrical center point of the active radiating area is set such that adegree of conversion along an optical path length of the light radiationis substantially 50%.

In accordance with again another feature of the invention, the lightsource is a surface-mounted component.

In accordance with again a further feature of the invention, the fillingcontains a resin material, in particular an epoxy resin. In a preferredembodiment, also, the basic body contains a thermoplastic material.

In accordance with yet an added feature of the invention, there isprovided:

a first leadframe carrying the LED at a first electrical contact areathereof;

a second leadframe connected to a second electrical contact area of theLED by a bond wire; and

wherein the basic body is produced by injection molding around theleadframes.

In accordance with yet an additional feature of the invention, therecess is defined by sloping and reflective side walls.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin LED light source with a lens, it is nevertheless not intended to belimited to the details shown, since various modifications and structuralchanges may be made therein without departing from the spirit of theinvention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section through an exemplary prior art embodimentof an LED light source with a lens glued on; and

FIG. 2 is a vertical section through an embodiment of an LED lightsource according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the figures of the drawing in detail, there is shown inFIG. 2 an embodiment according to the present invention wherein the samereference numerals are allocated for identical and functionallyidentical elements as in the above description of the light source ofFIG. 1. All the advantageous features mentioned with reference to theform of construction of FIG. 1 can also be used in the case of the formof construction according to the invention of FIG. 2.

The light source according to the invention of FIG. 2 solves the statedproblem in that the path length of the light radiation in the resinfilling 3 is unified. To achieve this, the resin filling 3 is producedwith a convex surface 3A, which has essentially the same distance fromthe LED 2 at every point. The volumetric proportion of the convertermaterial contained in the resin filling is set such that an adequatelylarge fraction of the blue light radiation is converted into yellowlight radiation along this unified path length from the LED 2 to theconvex surface 3A of the resin filling 3, so that the radiation isperceived by the human eye as white-light radiation. Consequently, onaccount of the blue-yellow color mixing of the same proportions, atevery point of the convex surface 3A white light enters the lens 4located above it.

The lens 4, produced for example from polycarbonate, has by contrast aconcave surface 4A, which enters into a form fit with the convex surface3A of the resin filling 3.

The light source according to the invention as shown in FIG. 2 can beproduced in the following way:

An LED 2 is electrically connected in the way already described toleadframes 5 and the leadframes 5 are encapsulated by a thermoplasticmaterial in such a way that a basic body 1 is formed. The LED 2 islocated in a recess 1A of the basic body 1. To this extent, the methodhas already been described in the above-cited article by Möllmer andWaitl. Then, however, the resin material 3 is not made to fill therecess 1A up to the rim but only up to a precisely fixed filling heightbelow it. Then, a prefabricated lens 4, which has the form shown in FIG.2 with the concave underside 4A, is inserted into the still liquid resinmaterial 3, the surface of the resin filling coming into contact withthe concave underside 4A of the lens 4, so that as a result the convexsurface 3A of the resin filling 3 is produced. After the lens 4 has beeninserted, the resin filling is cured.

The amount of resin material 3 with which the recess 1A is filled mustbe set as accurately as possible in such a way that the missing volumeup to the rim of the recess 1A corresponds to the displacement volume ofthe portion of the lens 4 forming the concave underside 4A.

The form of the convex surface 3A of the resin filling 3 and of theconcave underside 4A of the lens 4 is already fixed in the production ofthe lens 4. The condition, which this form has to meet is that thedistance of the actual light source, that is the active radiating areaof the LED, from these surfaces is constant. For this purpose, theactive radiating surface of the LED may be assumed to be punctiform andsituated at the center point of the active radiating area.

It should be understood that the present invention is not restricted tothe SMT form of construction represented in FIG. 2. For example, thebasic body may also be formed by a metallic block, such as a copperblock, which has a recess, on the bottom face of which the LED ismounted with one of its electrical contact areas, so that the copperblock is at the same time a heat sink and electrical terminal. The otherelectrical terminal could then be formed on an outer surface of thecopper block with an insulating layer lying in between, this electricalterminal being connected to the other contact area of the LED by abonding wire before the resin filling operation.

1. An LED light source, comprising: body having a recess formed therein;an LED for emitting light of a first wavelength; a filling; a convertersubstance for at least partially converting said light emitted by saidLED into light having a second wavelength and mixing said light of saidfirst wavelength and said light of the second wavelength; and a lensbeing prefabricated separate from said body and said filling and havinga concave underside, said LED being disposed in said recess and embeddedin said filling, said converter substance being contained in saidfilling, said lens being disposed in said recess of said body, and saidfilling having a convex surface being brought into a form fit with saidconcave underside of said lens by bringing said filling into contactwith said concave underside of said lens before the filling is finallycured, wherein said convex surface of said filling and said underside ofsaid lens are formed to have a substantially constant distance from saidLED.
 2. An LED light source, comprising: body having a recess formedtherein; an LED for emitting light of a first wavelength; a filling; aconverter substance for at least partially converting said light emittedby said LED into light having a second wavelength and mixing said lightof said first wavelength and said light of the second wavelength; and alens being prefabricated separate from said body and said filling andhaving a concave underside, said LED being disposed in said recess andembedded in said filling, said converter substance being contained insaid filling, said lens being disposed in said recess of said body, andsaid filling having a convex surface being brought into a form fit withsaid concave underside of said lens by bringing said filling intocontact with said concave underside of said lens before the filling isfinally cured, wherein said LED has an active radiating area and saidconvex surface of said filling and said underside of said lens areformed at a substantially constant distance from a geometrical centerpoint of said active radiating area of said LED.
 3. An LED light source,comprising: a body having a recess formed therein; an LED disposed insaid recess for emitting light of a first wavelength; a fillingembedding said LED, said filling having a converter substance for atleast partially converting the light emitted by said LED into lighthaving a second wavelength, said light of the first wavelength and saidlight of the second wavelength being mixed; and a lens in contact withsaid filling, said lens having a concave underside, whereby an upperside of said filling enters into a form fit with said concave undersideof said lens and has a convex surface fox-rued by said underside of saidlens, wherein a distance of said convex surface from said LED is setsuch that a degree of conversion along an optical path length of lightradiation is substantially 50%.
 4. An LED light source, comprising: abody having a recess formed therein; an LED disposed in said recess foremitting light of a first wavelength; a filling embedding said LED, saidfilling having a converter substance for at least partially convertingthe light emitted by said LED into light having a second wavelength,said light of the first wavelength and said light of the secondwavelength being mixed; and a lens in contact with said filling, saidlens having a concave underside, whereby an upper side of said fillingenters into a form fit with said concave underside of said lens and hasa convex surface formed by said underside of said lens, wherein said LEDhas an active radiating area and a distance of said convex surface froma geometrical center point of said active radiating area is set suchthat a degree of conversion along an optical path length of lightradiation is substantially 50%.
 5. An apparatus comprising: a bodyhaving a recess formed therein; an LED disposed in said recess foremitting light of a first wavelength; a filling embedding said LED andincluding a converter substance for at least partially converting thelight emitted by said LED into light having a second wavelength, saidlight of the first wavelength and said light of the second wavelengthbeing mixed when they emerge from the filling; and a lens in contactwith said filling, said lens having a concave underside, wherein saidfilling is in a fluid state that fills space between said LED and saidconcave underside of said lens.
 6. The apparatus according to claim 5,wherein a volume of said filling is less than a free volume of saidrecess with said LED disposed therein.
 7. The apparatus according toclaim 5, wherein said convex surface of said filling and said undersideof said lens are formed to have a substantially constant distance fromsaid LED.
 8. The apparatus according to claim 5, wherein said LED has anactive radiating area and said convex surface of said filling and saidunderside of said lens are formed at a substantially constant distancefrom a geometrical center point of said active radiating area of saidLED.
 9. The apparatus according to claim 5, wherein said LED is a bluelight-emitting LED based on GaN and said converter substance isconfigured to convert light radiation in a blue spectral range intolight radiation in a yellow spectral range.
 10. The apparatus accordingto claim 5, wherein said LED is a UV-emitting LED and said convertersubstance converts UV light into a visible spectral range.
 11. Theapparatus according to claim 5, wherein said LED is a surface-mountedcomponent.
 12. The apparatus according to claim 5, wherein said fillingcontains a resin material.
 13. The apparatus according to claim 5,wherein said body contains a thermoplastic material.
 14. The apparatusaccording to claim 5, which further comprises: a first leadframecarrying said LED at a first electrical contact area thereof; a secondleadframe connected to a second electrical contact area of said LED by abond wire; and wherein said basic body is produced by injection moldingaround said first and second leadframes.
 15. The apparatus according toclaim 5, wherein said recess is defined by sloping and reflective sidewalls.
 16. The apparatus according to claim 5, wherein said filling hasa common component extending from the LED to the concave underside ofthe prefabricated lens.